Electrical integration circuit



March 1952 w. A. HIGINBOTHAM 2,589,807

ELECTRICAL INTEGRATION CIRCUIT Filed Jan. 24, 1945 GATE GENERA TOR VAR/ABLE E DELAY C/RCUI r uv ur WA v5 GENE/7A TOR TIMER INVENTOR.

W/L L /AM A. H/G/NBOTHA M Patented Mar. 18, 1952 r rice ELECTRICALINTEGRATION CIRCUIT William A. Higinbctham, Santa Fe, N. Men, as-

signor, by mesne assignments, to the United States of America asrepresented by the Secretary of War Application January 24,1945,:SerialNo; 574,374

Claims. 1

'Thisiinvention relates to an electrical apparatus and'mcre particularlyto a'wave modifying circuit adaptedtoperform'integration operations.Morespecifically, the circuit is adapted to develop :an outputwave formrepresenting an integration of an input wave form.

One object of the invention is to provide such a circuit whereby theoutput wave form represents an integration of a waveform which is aselected function of "an independent variable.

Another object is to provide such a circuit whereby :a desired outputvoltage may be developed.

A further object contemplates the production of suchoutput wave formsbetween predetermined limits of :an independent variable.

The'apparatus herein has'many applications and, as an example, it may beused in cathode ray tube deflection voltage circuits of radio objectdetecting and ranging systems.

The apparatus here disclosed operates to generatea recurring output wavein which each'wave' -form represents an integration of an input waveform. Thus, the amplitude of an out ut wave form atany instantrepresents'an evaluation at that-instant of'the inte ration of the inputwave form-from a lower limit wh ch may bepredetermined-as will'appearhereinafter. The amplitudes of thewave-forms are functions of anindependent variahlewhich is represented by a time axis, the initiationof each input wave form corresponding to zero value of the independentvariable.

Atypical use of this integrating circuit may be to generate, asshownin'the communication s stem describedin the patent-to Luis W. Alvarez,Patent *No. 2,480,208, -fi'ed June 27, 1944, and issued August 30, 1949,recurring output wave forms each having a voltage which is proportionalto the algebraic expression 1 -71 In'this expression, 1 (range) is theindependent variable, andh (height) is a constant whose value may bevaried as desired. The expression r -h is itself proportional to anintegration, from a lower limit 71.. of a voltage which varies linearlywith r. As-r is represented by time, the voltage of the input wave formused herein varies linearly with time and may be produced by a saw-toothgenerator.

In the drawing:

Fig. 1 is a diagram, partly in block representation, of a circuit whichwill perform integrations upon an input wave form;

Figs. 2 and 3 are dia rams showing wave forms present in various partsof the circuit; and

Fig. 4 is a diagram of a typica output voltage wave form produced by thecircuit from a selected input wave form.

Referring now to Fig. l, the present integrating circuit includesseveral components which are well .known :to the :art and are thereforerepresentedinblockiorm. Such components will-not be dealt with in detailexcept insofar as is necessary to describe the present invention.Reference :numeral :5 designates a timer which produces-recurringtriggervoltage pulses 6 of relatively short duration, for example,-2 or3 microseconds. These trigger pulses are applied ,toian input wavegenerator I :to time or trigger the production of voltage waves having apredetermined form. Suchan input-Waveformmay as mentioned above, have avoltage which varies linearly with timeasshown at 8.

The :wave forms shown on-the diagram in Fig.1 are drawn in theirrelative positions along 13a common time base. For examplewave form8 isshown astinitiated at the instant of occurrence of a trigger ,6. Therepetition rate of the trigger pulses 6 and the'time duration'of theinput waves 8, if desired, may be such as to space the input waves alongthe time axis by a time duration equal to or, greater thanthe durationof an input wave.

A lead [0 from input wa-ve generator l-applies the 'voltage'wave form 8to a control grid llof a vacuum tube H2. The control grid H is connectedthrough a resistance l3 to a ground point of the circuit. The tube I2may be-of pentode type as shown, having ascreen grid 14130 which isapplied apositive voltage of constant value. A suppressor grid l5 and acathode l6-are connected together and througha biasing resistance I! toground. Plate N3 of the tube ['2 is connected to one terminal ofarelativey large capacitance 19 at a junction 2G,-the other terminal ofthe-capacitance being connected to a junction 25. A positive voltage ofconstant value is applied, as shown, to the'junction 25 from a sourcehaving a low impedance to ground for alternating voltage components. I

During circuit operation, a recurring unidirectional current is producedin the plate IB-capacitance I9 circuit due to the recurring inputvoltage applied to the control grid ll, and to the periodic discharge ofthe capacitance I9, as will be presently described.

As will appear hereinafter, the pate potential at the junction .23undergoes variations which, however, are small compared to the constantvoltage applied to the junction 25. The tube l2 is of the constantcurrent.type whose characteristic is that. despite'such variations ofplate potential, the plate current is substantially dependent only uponthe voltage applied to the control grid I l. The operating conditions ofthe tube 12 are such as tosecure a linear relation between its platecurrent and control grid votage, the variation of plate voltage havingnegligible efiect on this relationship overthe range of operation. Thus,th e varying currentproduced in the .delay circuit 55.

.the voltage wave 8 applied to the control grid H causes a correspondingelectron current wave to flow in the cathode-plate circuit of tube I2.As will appear hereinafter, a selected time-portion of this currentflows through the integrating capacitance 19 in the direction ofjunction 20 to junction '25, resulting in an integration voltage wave atthe terminal with respect to terminal 20. Junction 25 is effectively atground potential so far as varying voltages are concerned, so that avoltage wave 30, which is an inversion of the desired integration Waveform, is present at terminal 20.

' The voltage wave appearing at the junction 20 is communicated to acontrol grid 3| of an amplifier vacuum tube 32 through a couplingvcapacitance 33; The control grid 3| is connected through a resistor 34to ground. Vacuum tube 32 may be of triode type as shown, having a plate35 which is connected to a junction 36 and thence through resistance 31to the positive potential at the junction 25. Cathode 38 of the vacuumtube 32 is connected through a biasing resistance 39 to ground. Theoperation of the vacuum tube .32 is linear, and the varying potentialdeveloped at the junction 36 is an inverted replica of the voltage wave30 applied to the grid 3|. Junction 36 may be connected, as shown, to anoutput terminal 40 through a coupling capacitance M.

A voltage wave 42 at the terminal 40 is thus the desired integration ofthe input voltage wave form applied to the control grid 1 I of the tube12. As mentioned previously, the capacitance I9 is periodicallydischarged and maintained in a ,short-circuited condition for apredetermined time interval in order that recurring waves of voltage maybe formed at the junction 20. Additionally, by causing the capacitanceto become unshorted at a selected time after initiation of each inputwave form, the output voltage wave willrepresent an integration of theinput wave from a lower limit represented by that selected time. This isaccomplished in the following manner.

The trigger pulses 6, in addition to being applied to generator i, arealso applied to a variable Here a selected time delay, representing, forexample, the quantity h previously mentioned, is imposed on the triggerpulses 6 resulting in time-displaced trigger pulses 5!. The timeinterval between the original and delayed trigger pulses may be variedas desired by a control 52, which adjusts circuit constants within thesaid variable delay circuit to produce the predetermined time delay. Thesaid control 52 may be adjustable manually, or automatically, inresponse to some condition. As shown in the previously mentionedcopending application. for example, such apparatus may be mounted in anaircraft, and a height-responsive device may, by suitable linkage,position the control 52. V

' The delayed trigger pulses 5! are applied to a gate generator 53 totime or trigger the cycles of a rectangular wave 54, said rectangularwave therefore having the same frequency as the input voltage 8. Therelatively negative and positive portions of rectangular wave 54 mayhave equal time durations (or they may have unequal time durations), andthese portions will hereinafter be termed negative and positive gates,respectively. The gate generator is so designed that the leading edge ofa negative gate is produced by, and is thus in time-phase with, adelayed trigger pulse 5|.

A lead 55 from the gate generator 53 applies the rectangular wave 54 toa control grid 56 of a vacuum tube 51. Tube 51 may be of triode type asshown, having a plate 58 and a cathode 59 connected to the junctions 25and 20, respectively, of the capacitance IS. The potential of thecontrol grid 56 with respect to'the cathode 59 determines Whether or notthe tube 51 forms a short circuit across the integrating capacitance I9,and the tube 51 is therefore referred to as a switch tube.

Thus a positive gate of wave 54 causes the tube to conduct andeffectively short circuit capacitance I9. A negative gate portion of therectangular wave causes removal of the efiective short circuit acrossthe integrating capacitance, and

the plate current of the tube [2 will at such time become a chargingcurrent for the integrating capacitance.

This condition is shown in greater detail in Figs. 2 and 3, in which arectangular wave applied to switch tube 51, and a charging current ofcapacitance l9, respectively, are drawn to the same time scale indicatedby the horizontal axes designated t. The vertical axes of Figs. 2 and 3represent voltage and charging current, respectively, so designated byreference characters '1; and i.

Referring again to tube [2, there is at all times during the time of aninput wave 8 a continuous path for current flow through said tube,the'plate circuit being completed either through switch tube 57 duringthe time of a positive gate, or through capacitance l9 during the timethat switch tube 51 is open-circuited by a negative gate. The dottedline of Fig. 3 represents that time-portion of plate current of tube l2which is bypassed around capacitance l9 by switch tube 51 during thedelay time interval corresponding, in the example given, to the quantityh. The occurrence of the leading edge of a negative gate (positionedalong the time axis by variable delay circuit 50) thus determines thelower limit of the integration operation performed by the presentcircuit.

The resultant voltage developed, in this instance. across capacitance I9is shown in Fig. 4, in which the axis designated V is a voltage axis.The wave form shown is proportional to an in tegration of the input waveform from the preselected lower limit it and is thus proportional. asstated above, to the desired expression r 'h This is also the wave formof the output voltage appearing at the terminal 441 as explainedheretofore.

While there has been illustrated and described herein, but rather it isto be taken as defined it is apparent that variations and modificationsmay be made by those skilled in the art. It is to be understood that thescope of the invention is not to be limited to the precise detailsdisclosed herein one embodiment of the present invention. by thefollowing claims.

I claim:

1. A voltage generator including a source ofrecurring input voltagewaves, each input voltage wave representing a function of an independentvariable, a vacuum tube having at least a cathode, control grid andanode, an output circuit for said vacuum tube, said output circuitincluding a capacitance and normally closed switch means connected inparallel therewith, said source being connected to said control gridwhereby input voltage waves are applied to said control grid, saidvacuum tube being adapted to provide a recurring current wave in saidoutput circuit, said current corresponding in form to said input voltagewave, a timing means, said timing means connected to said source andadapted to initiate each input wave, a variable delay circuit connectedbetween said timing means and said switch means, said variable delaycircuit cooperating with said timing means to open-circuit said switchmeans at a predetermined time after initiation of each input voltagewave, whereby a recurring output voltage wave is developed across saidcapacitance, said output voltage wave representing a definiteintegration of said function, the lower limit of integrationcorrespondin to said predetermined time after initiation of each inputvoltage wave.

2.,A voltage generator including a source of recurring input voltagewaves, each input voltage wave representing a function of an independentvariable, a vacuum tube having at least a cathode, control grid andanode, an output circuit for said vacuum tube, said output circuitincluding a capacitance and normally closed switch means connectediniparallel therewith, said source being connectedto said control gridwhereby input voltage waves are applied to said control grid, saidvacuum tube being adapted to provide a recurring current wave in saidoutput circuit, said current wave correspondin in form to said inputvoltage wave, and means "for opening said switch means after apredetermined time interval to permit a recurring output voltage wave tobe periodically developed across said capacitance, said output voltagewave representing a definite integration of said function, the lowerlimit of integration corresponding to said predetermined time interval.

3. In an electronic integrating circuit of the character describedhaving applied thereto a recurring input voltage wave, a vacuum tubehaving at least a cathode, control grid and anode, an output circuit forsaid vacuum tube, said output circuit includin a capacitance and switchmeans connected in parallel therewith, said control grid having appliedthereto said input voltage wave, said vacuum tube being adapted toprovide a recurring output current wave in said output circuit, saidcurrent wave corresponding in form to said input voltage wave, means forcausing said switch means to short said capacitance until apredetermined time after initiation of each input voltage wave and to beunshorted during the remaining time of each input voltage wave, wherebya recurring output voltage wave is developed across said capacitance,said output voltage wave representing an integration of said inputvoltage wave from a lower limit corresponding to said predetermined timeafter initiation of each input voltage wave.

4. A voltage generator including a source of recurring input voltagewaves, each input voltage wave representing a function of an independentvariable, a first vacuum tube having at least a cathode, control gridand anode, an output circuit for said vacuum tube, said output circuitincluding a capacitance and normally closed switch means connected inparallel therewith, said switch means comprising a second vacuum tubehaving at least a cathode, a control grid and an anode, the saidcapacitance bein connected between said cathode and said anode, saidsource being connected to the control grid of said first vacuum tubewhereby input voltage waves are applied to said control grid, said firstvacum tube being adapted to provide a recurring current wave in saidoutput circuit, said current wave corresponding in form to said inputvoltage wave, a timing means, said timing means being connected to saidsource and adapted to initiate each input wave, a gate generator havingits output connected to the control grid of said switch means and avariable delay circuit connected between said gate generator and saidtiming means, said variable delay circuit cooperating with said timingmeans and said gate generator to open-circuit said switch means at apredetermined time after initiation of each input voltage wave, wherebya recurring output voltage wave is developed across said capacitance,said output voltage wave representing a definite integration of saidfunction, the lower limit of integration corresponding to saidpredetermined time after initiation of each input voltage wave, and avacuum tube amplifier having at least a cathode, a control grid and ananode, the said capacitance being connected in the grid-anode circuit ofsaid amplifier, whereby the said output voltage wave may be amplified.

5. In an electronic integrating circuit of the character describedhaving applied thereto a recurring input voltage wave, a vacuum tubehaving at least a cathode, control grid and anode, an output circuit forsaid vacuum tube, said output circuit including a reactance and switchmeans connected in parallel therewith, said control grid having appliedthereto said input voltage wave, said vacuum tube being adapted toprovide a recurring current wave in said output circuit, said outputcurrent wave corresponding in form to said input voltage wave, means forcausing said switch means to short said reactance until a predeterminedtime after initiation of each input voltage wave and to be unshortedduring the remaining time of each input voltage wave, whereby arecurring output voltage wave is developed across said reactance, saidoutput voltage wave representing an integration of said input voltagewave from a lower limit corresponding to said predetermined time afterinitiation of each input voltage wave.

WILLIAM A. HIGINBOTHAM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,188,970 Wilson Feb. 6, 19402,212,967 White Aug. 27, 1940 2,241,619 Sherman May 13, 1941 2,282,340Pieplow 1- May 12, 1942 2,300,189 Wolff Oct. 27, 1942 2,414,486 RiekeJan. 21, 1947 2,489,312 Pacini 1 Nov. 29, 1949

